In making color proof (or pre-press proof) utilizing photopolymers, two methods have so far been employed, i.e., the overlay method and the surprint method. The overlay method comprises the preparation of two or more color proofing sheets wherein each has a transparent support upon which is a separation image with one of the colors necessary for full color reproduction. Those sheets are superposed upon one another (the thus superposed sheet sandwich is called a color test sheet) to undergo color proofing. According to this method, a multicolor image can be formed in every color proofing procedure by superposing color proofing sheets with two to four different colors upon one another. Therefore, the method is advantageous in that it is convenient and can be used for continuous inspection.
On the other hand, the surprint method consists of forming separation images with individual colors one after another on one support to produce therefrom a multicolor image. A problem of the overlay method, namely the color reproduced by superposing color proofing sheets is more or less attended with distortion, is avoided by the surprint method so image quality more similar to the original is obtained in the graphic arts.
The surprint method can be accomplished in two ways, by color material-incorporation or by color material-supply. The color material-incorporation variation has as a merit in that the color density stability of said color proofing sheet is especially excellent because the color proofing sheet contains color material layers that are colored in advance, in contrast with that of color material-supplied variation in which color density of a color test sheet varies among manufacturers. Details of the production of color proofing sheets according to surprint methods are described, e.g., in JP-A-59-97140 (corresponding to U.S. Pat. No. 4,482,625), JP-A-61-188537, JP-A-63-2038, JP-A-63-2039 and so on (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
A color proofing sheet described in detail in the above-cited patent specifications is a light-sensitive laminate, in which a peeling layer comprising organic polymers, a color material layer and a light-sensitive layer are laminated on a support, in that order, to form a light-sensitive material.
It is required of a peeling layer in such a light-sensitive transfer sheet as described above that in undergoing thermal transfer, the peeling layer can be peeled from the temporary support in a good condition, and that adhesiveness among nonimage parts of individual colors (peeling layers) and to each image part are sufficient.
To answer the above-described requirement, it is particularly desirable that alcohol-soluble polyamides such as copolymerized nylon, N-alkoxyalkyl-substituted nylon and the like be used. However, in the independent use of an alcohol-soluble polyamide the facility in peeling from the support tends to undergo the influence of humidity and, under high humidity in particular, poor transfer sometimes occurs because of increased adhesiveness to the support.
To solve this problem, it is desired that an alcohol-soluble nylon be used in combination with an alkali-soluble organic polymer, such as styrene-maleic acid copolymer, polyhydroxystyrene or the like, as disclosed in JP-A-61-188537, JP-A-63-2039 and so on. Even in the color proofing sheet prepared in accordance with the methods described therein, it sometimes happens that the peeling layer deteriorates with the lapse of time to cause poor transfer thereby resulting in deterioration of image quality.